An optical instrument known as a coronagraph was originally invented to observe the sun's corona at times other than when there is a solar eclipse. This type of optical instrument has since been used in other astronomical applications to help obtain an optical image of low intensity object(s) (e.g., planet(s)) that are located in close proximity to a high intensity object (e.g., sun). In addition, this type of optical instrument could be used in military applications to help obtain an optical image which can be used to identify low intensity object(s) (e.g., missile(s)) that are located in close proximity to a high intensity object (e.g., sun or other infrared source). Two traditional optical instruments 100 and 200 are described next with respect to FIGS. 1 and 2.
Referring to FIG. 1 (PRIOR ART), there is shown a diagram of a traditional optical instrument 100 which has been setup to obtain an optical image 102 of three low intensity objects 104 (e.g., three planets 104) that are located in close proximity to a high intensity object 106 (e.g., sun 106) (note: the high intensity object 106 does not appear in the final optical image 102). As shown, the traditional optical instrument 100 includes an imaging device 108 (e.g., refractive imaging device 108, reflective imaging device 108), a pick-off mirror 110 and a re-imaging device 112 (e.g., refractive re-imaging device 112, reflective re-imaging device 112). The pick-off mirror 110 has a surface 115 with a hole 116 extending there through which functions like an occulting mask to re-channel light 111 associated with the sun 106 away from the light 113 associated with the three planets 104 (see the front view of the pick-off mirror 110).
In this example, the imaging device 108 has been positioned to receive an image 114 that contains light 111 associated with the sun 106 and also contains light 113 associated with each of the three planets 104. Plus, the pick-off mirror 110 has been positioned on an optical path 117 (at an intermediate focal plane) to receive the image 114 from the imaging device 108. In particular, the pick-off mirror 110 has been positioned such that the hole 116 receives a portion of the image 114 containing the light 111 associated with the sun 106 and re-channels this light 111 off the optical path 117 and away from the re-imaging device 112. In addition, the pick-off mirror 110 has been positioned such that a part of the surface 115 which does not have the hole 116 therein receives a portion of the image 114 containing the light 113 associated with the three planets 104 and reflects that portion of the image 114 on the optical path 117 towards the re-imaging device 112. Upon receiving the light 113 reflected from the pick-off mirror 110, the re-imaging device 112 generates the desired optical image 102 that contains the light 113 associated with the three planets 104 but does not contain the light 111 associated with the sun 106 (note: the desired optical image 102 is focused on the focal plane 120 which is located on the optical path 117).
Referring to FIG. 2 (PRIOR ART), there is shown a diagram of another traditional optical instrument 200 which has been setup to obtain an optical image 202 of three low intensity objects 204 (e.g., three planets 204) that are located in close proximity to a high intensity object 206 (e.g., sun 206) (note: the high intensity object 206 does not appear in the final optical image 202). As shown, the traditional optical instrument 200 includes an imaging device 208 (e.g., refractive imaging device 208, reflective imaging device 208), a pick-off mirror 210 and a re-imaging device 212 (e.g., refractive re-imaging device 212, reflective re-imaging device 212). In this case, the pick-off mirror 210 has a surface 215 where a portion of which has one or more opaque spots 216 (only one shown) which function like an absorptive occulting mask and absorb light 211 associated with the sun 206 while not affecting the light 213 associated with the three planets 204 (see the front view of the pick-off mirror 210).
In this example, the imaging device 208 has been positioned to receive an image 214 that contains light 211 associated with the sun 206 and also contains light 213 associated with each of the three planets 204. Plus, the pick-off mirror 210 has been positioned on an optical path 217 (at an intermediate focal plane) to receive the image 214 from the imaging device 208. In particular, the pick-off mirror 210 has been positioned such that the opaque spot(s) 216 receives a portion of the image 214 containing the light. 211 associated with the sun 206 and absorbs this light 211 such that it will not be reflected on the optical path 217 towards the re-imaging device 212 (note: the opaque spot(s) 216 is typically an adsorptive material which can be rather difficult to apply in a precise manner on the surface 215 of the pick-off mirror 210). In addition, the pick-off mirror 210 has been positioned such that a part of the surface 215 not covered by the opaque spot(s) 216 receives a portion of the image 214 containing the light 213 associated with the three planets 204 and reflects that portion of the image 214 on the optical path 217 towards the re-imaging device 212. Upon receiving the light 213 reflected from the pick-off mirror 210, the re-imaging device 212 generates the desired optical image 202 that contains the light 213 associated with the three planets 204 but does not contain the light 211 associated with the sun 206 (note: the desired optical image 202 is focused on the focal plane 220 which is located on the optical path 217).
Although these two traditional optical instruments 100 and 200 function relatively well there is still a desire for an improved optical instrument that can be used to obtain an optical image of one or more low intensity objects (e.g., planets, missiles) that are located in close proximity to a high intensity object (e.g., sun). This need and other needs are satisfied by the present invention.